Spasticity, contracture, and muscle weakness commonly occur in conjunction with various neurological disorders such as stroke, spinal cord injury, poliomyelitis, cerebral palsy, amyotrophic lateral sclerosis, multiple sclerosis, muscular dystrophy, myasthenia gravis, and spinal muscle atrophy. These symptoms of spasticity, contracture, and muscle weakness are closely related to each other and are major factors contributing to disabilities in patients with such neurological impairments. If a method were available for determining in vivo biomechanical properties like fiber stress, fiber force, fiber tension, sarcomere length, sarcomere uniformity/non-uniformity, and number of sarcomeres in series of single muscle fibers or small bundles of muscle fibers, diagnosis and treatment of these symptoms could be substantially improved. If such a system could be used to determine in vivo biomechanical properties of other soft tissues such as ligament or tendon tissues, or brain or nerve fibers/axons, the functioning of these tissues could be more effectively analyzed and advancements in diagnosis and treatment of symptoms associated with injuries and impairments in such tissues also could be significantly advanced. For example, if the level of stress in externally accessible nerve fibers in the brain could be determined in vivo, it may be possible to better diagnose and treat neural-based maladies related to disturbances in the network of nerve fibers that pull the cortex into shape during brain development and hold it in place throughout life.
Current methods of examining properties of muscle fibers like fiber stress, sarcomere length and number of sarcomeres in series are inaccurate and unreliable because they must be performed in vitro and because they rely on methods like laser diffraction which yield only average sarcomere fiber length data. Most importantly, in vitro sarcomere length measurements have been shown to differ significantly from actual in vivo sarcomere lengths. Also, laser diffraction measurement of sarcomere length relies upon the production of diffraction lines produced by passing laser light through muscle fibers to produce a diffraction pattern from which average sarcomere lengths over a substantial area taking in a multiplicity of fibers and sarcomeres can be derived. The laser diffraction technique therefore does not permit precise determination of the length of selected sarcomeres in small isolated muscle fibers or fiber bundles and offers no opportunity for actually viewing and determining the lengths of the sarcomeres in muscle fibers of interest.
A system for examining in vivo biomechanical properties like fiber stress, sarcomere length and number of sarcomeres in series of single muscle fibers or small bundles of muscle fibers could lead to breakthroughs in the diagnosis and treatment of such neuromuscular disorders by demonstrating, inter alia, whether spastic fibers are under higher stress as compared to those of healthy subjects and the level of such stress, and whether sarcomeres in spastic muscles adapt to increased tension by adding more sarcomeres in series as in normal cases. If it were possible to examine sarcomere lengths at rest and under tension in vivo in a meaningful and reliable way, this would help guide and optimize treatment. In order to do this it is important to have accurate and economic methods and apparatus. The present invention provides such apparatus and methods for determining fiber stress, sarcomere length and number of sarcomeres in series under in vivo conditions. The present invention also provides apparatus and methods for determining tension and stress of collagen or other fibers as well as fiber arrangement in other soft tissue such as ligament, tendon tissues, and in brain and nerve fibers/axons.